The present invention relates generally to circuit and load protector devices, and more particularly to circuitry permitting extended range overload tripping while avoiding nuisance tripping due to load transients.
Numerous applications are known for electrical protective devices. In general, such devices may include circuit breakers, instantaneous trip devices of various natures, overload protective devices, and so forth. Improvements in such circuitry have tended to integrate various types of hardware and software in arrangements that provide both for the application of power and the protection of powered devices. One particularly important application of this type includes the drive of electric motors.
Electric motor drive circuitry and protection are afforded by a wide range of devices. A typical motor protection system includes fused interrupts, contactors, circuit breakers, and so forth. While such devices provide for effective application of power and interruption of power, they are not without drawbacks. For example, existing motor control circuitry typically includes a wide range of product offerings specifically designed for differently rated machines. The resulting family of products can be quite large, resulting in expense in system design, manufacturing and stocking, and reducing the versatility of the resulting products to the ultimate user.
Extended range devices may be provided, as set forth in the description below. However, such extended devices may suffer from nuisance tripping in certain circumstances, due to the algorithms employed for circuit and wiring protection. In particular, where protection is afforded by very rapid tripping parameters, nuisance tripping may result during certain periods of operation. In circuitry design for motor protection, for example, nuisance tripping may result during startup or other transient periods due to asymmetries in the load performance. It would be advantageous, therefore, to avoid such nuisance tripping, while providing for the other advantages of extended range operation.